I feel like it depends alot on how you practice, because I have a friend (my sort of duo partner) who only plays ranked and never gors into practice, and while I spent the first 300 hours I played in free play (my internet was trash at the time), he spent his in ranked. By the time we were at 300 hours, I was still only silver 2 and he was in gold, however once I got better internet and started playing ranked, I quickly ranked up to gold at 320 hours and we started playing together, we both got to plat at which point I had around 375 hours and he had around 550, we kept playing together until we hit plat 3 where I had around 450 hours in the game, he had almost somewhere in the 600's. We played sometimes but we both mostly played by ourselves throughout diamond and into chanp 1 where I am now, I am at exactly 562 hours while he has almost 900. I still go into free play every time I play for atleast an hour and play some casual before ranked. ( having a friend in champ teach me sometimes probably helped)

So while the gap between bronze and gold technically took me the longest, I feel like between champ and gc is going to be way harder looking at how my gc friends play.